1. Field
This disclosure relates generally to integrated circuits, and more specifically, to integrated circuits having a multi-layer source/drain stressor.
2. Related Art
One of the techniques for improving N channel and P channel transistor performance is by introducing strain to the channel. One of the techniques to introduce strain is to remove semiconductor material from the source/drain locations and regrowing a semiconductor material epitaxially which is of a different composition. For example, one approach for improving P channel performance, where the initial semiconductor material and thus the channel is just silicon, is regrowing a combination of silicon and germanium (SiGe) in the source/drain regions which exerts a compressive stress on the channel. One of the difficulties is that the amount of stress being exerted is dependent on the germanium concentration but increasing the germanium concentration can cause the formation of defects which then causes a reduction in the stress being exerted. In addition, as the device dimension shrinks during the technology evolution, one critical challenge is to maintain good performance characteristics for short channel transistors.
Thus, there is a need for improving on the technique for regrowing the source/drains to provide stress to the channel.